Semiconductor devices include metal layers that are insulated from each other by dielectric layers. As device features shrink, reducing the distance between the metal lines on each layer, capacitance increases. The parasitic capacitance may contribute to effects such as RC delay, power dissipation, and capacitively coupled signals, also known as cross-talk. To address this problem, insulating materials that have relatively low dielectric constants (referred to as low-k dielectrics) are being used in place of silicon dioxide (and other materials that have relatively high dielectric constants) to form the dielectric layer that separates the metal lines.
Organic polymers have been used as insulating materials because their dielectric constants tend to be less than that of silicon dioxide, the most commonly used insulator. However, organic polymers typically suffer from lower mechanical strength and lower hardness than silicon dioxide. One measure of the mechanical strength or hardness is Young's modulus, also referred to as the modulus of elasticity (E).
One example of a material that may be used to form a low-k dielectric layer is carbon doped oxide (CDO). A CDO layer may be deposited on a substrate using a plasma-enhanced chemical vapor deposition (PECVD) process, for example. Spin-on carbon-doped oxide materials used to form insulating layers typically have low dielectric constants, often less than 2.0, but the modulus of elasticity (E) of such materials may be in the range of 1 to 3 GigaPascals (GPa).
In general, the modulus is a function of the material density, where E=(E0) (ρm). In this equation, E represents the predicted modulus, E0 represents the modulus of the dense matrix, ρ represents the density which is proportional to porosity and the dielectric constant (k), and m represents an experimentally determined exponent.
Dielectric materials with low dielectric constants (below about 2.0) tend to be at least 50% porous and typically have low mechanical strength. For example, carbon doped oxide (CDO) that is 58% porous has a calculated modulus of 3.0 GPa. Silicon dioxide (SiO2) that is approximately 71% porous has a calculated modulus of 5.5 GPa. Fluorine doped silicon dioxide (SiOF) that is approximately 63% porous has a calculated modulus of 5.3 GPa. Low-k dielectric materials tend to be relatively brittle, and/or tend to crack or flake when exposed to stress. Their low mechanical strength limits or prevents their use for very thin films, such as those thinner than about 1 micron.
Accordingly, there is a need for a semiconductor device having a low-k dielectric layer with greater mechanical strength. Mechanical strength of at least about 8 GPa is considered desirable for semiconductor manufacturing processes. There is a need for an improved process for making such a semiconductor device.